This invention concerns a structure for anchoring a rod, pile or the like (hereinafter called a "rod" or "anchor rod") into concrete, rock or similar material (hereinafter called "concrete") by means of a cementing material such as a resin adhesive.
Such an anchoring method is commonly used for fixing structural members, machinery, equipment, temporary structures and the like in concrete. A typical such structure anchoring is illustrated in FIG. 6 (a). As shown in this figure, an anchor rod 1 is fixed in concrete 3 by means of a cementing material 2 which fills the empty portion of an anchor hole 4. FIGS. 8 and 9 respectively illustrate a deformed bar and a threaded bolt which are anchored by this method. The cementing materials which are normally used include epoxy resins, polyester resins and non-contracting cement.
This anchoring method has the advantages that a high positioning accuracy is easier to attain than with other methods, it provides a high-strength anchorage, and it can be rapidly performed. For these reasons, it has been acquiring increasing acceptance in various fields. For example, in the field of civil construction, it is used for anchoring bridge supports, bridge pier studs and shutter supports. In the field of architectural construction, it is used for anchoring exterior equipment, piping brackets, slab reinforcement elements, exterior sign boards and other members.
However, this method can still not be said to have become well established. Reliable design criteria for it are not yet available. Although not very often, pullingout of an anchor and/or concrete fracture around an anchor actually occurs, especially with larger anchors whose failure is very serious. The reasons for such failures may be related to inadequacies in anchor design.
One of the unique features of these pullout fractures or concrete fractures is that, as shown in FIG. 6 (b), the anchor 1 is pulled out together with a cone-shaped piece of concrete 6 (hereinafter called a "cone"), the anchor and the cone 6 resembling the shape of a mushroom.
As a result, a crater-shaped hole is produced in the surface of the concrete body. The hole decreases the load bearing capacities of the nearby anchors, can cause them to fail, and can finally even cause the object which is supported by the anchors to fall down.
One of the reasons why such troubles occur more often with larger anchors may be attributable to the fact that it is very difficult to test larger anchors and there is not so much laboratory or field testing data on them. In many cases, larger anchors have been designed by extrapolating data for smaller anchors on which testing is far easier to conduct and for which much data is readily available.